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R C Ford

Publications and source records attributed to R C Ford.

At least 37 records · Page 2Linked to original sources
PubMed1996

A current assessment of photosystem II structure.

This review covers the recent progress in the elucidation of the structure of photosystem II (PSII). Because much of the structural information for this membrane protein complex has been revealed by electron microscopy (EM), the review will also consider the specific technical and interpretation problems that arise with EM where they are of particular relevance to the structural data. Most recent reviews of photosystem II structure have concentrated on molecular studies of the PSII genes and on the likely roles of the subunits that they encode or they were mainly concerned with the biophysical data and fast absorption spectroscopy largely relating to electron transfer in various purified PSII preparations. In this review, we will focus on the approaches to the three-dimensional architecture of the complex and the lipid bilayer in which it is located (the thylakoid membrane) with special emphasis placed upon electron microscopical studies of PSII-containing thylakoid membranes. There are a few reports of 3D crystals of PSII and of associated X-ray diffraction measurements and although little structural information has so far been obtained from such studies (because of the lack of 3D crystals of sufficient quality), the prospects for such studies are also assessed.

Microscopy, Electron↗
PubMed1994

Photosystem I: Structural and functional studies.

In this article we describe the current knowledge of the structure of photosystem I, in particular the cyanobacterial form of this photosynthetic complex. We also describe recent experiments on the stability of the complex in detergents and denaturants and discuss the results in relation to the functional properties of the complex in electron transport across the thylakoid membrane.

Absorption↗
PubMed1992

Detergent sensitivity of the tonoplast H(+)-ATPase and its purification from Beta vulgaris.

Tonoplast membrane fractions were isolated from beetroot (Beta vulgaris) using a refined method of preparation which significantly improved the yield of active tonoplast H(+)-ATPase, and electron microscopy showed these fractions to be a preparation of small vesicles, of diameter 500 nm to 50 nm and a minor fraction consisting of mainly tubular membrane structures of diameter 5 nm and length up to 1 micron. The stability of the tonoplast H(+)-ATPase was assessed in the presence of many biological detergents, using a linked assay. The addition of detergent to tonoplast membranes generally led to an increase in ATPase activity, and activity was maintained in a wide range of both non-ionic and zwitterionic detergents. Using the non-ionic detergent dodecyl maltoside, the tonoplast H(+)-ATPase was partially purified using ion-exchange chromatography on an HPLC system. Very high rates of ATP hydrolysis were recorded in these fractions. The purified membranes behaved as expected in the presence of known activators and inhibitors. An unexpected observation, however, was that low concentrations of vanadate could significantly increase the rate of H(+)-ATPase activity.

Detergents↗
PubMed1992

Analysis of the structure of photosystem I in cyanobacterial thylakoid membranes.

Using electron microscopy of negatively stained specimens, we have investigated the shape and degree of association of photosystem (PS) I complexes in cyanobacterial thylakoid membranes. When incubated at high concentrations of magnesium chloride (greater than 0.15 M), the PSI complexes form small ordered arrays in the membrane composed of monomeric complexes in a P1 square lattice of dimensions a = b = 11 nm. Averaged projections of the complex resemble those found for the purified PSI reaction centre after reconstitution (Ford, R.C, Hefti, A. and Engel, A. (1990) EMBO J. 9, 3067-3075). Some small differences in its shape are discussed, with particular reference to the differences in the polypeptide composition of the 2 preparations. We find that the complex remains in the monomeric form in the thylakoid membrane under all the conditions tested.

Cyanobacteria↗
PubMed1990

Ordered arrays of the photosystem I reaction centre after reconstitution: projections and surface reliefs of the complex at 2 nm resolution.

We present an electron microscopical analysis of the photosystem I reaction centre, the membrane complex involved in the second light-driven step of photosynthetic electron transfer in plants and cyanobacteria. To this end, ordered two-dimensional arrays were reconstituted from detergent solubilized photosystem I reaction centres and phospholipids, and studied by electron microscopy and digital image processing. Small (P1) and large (P3) hexagonal lattices obtained with reaction centres of the thermophilic cyanobacterium Phormidium laminosum had unit cell sizes of a = b = 8.8 nm and 15.8 nm, respectively. Reaction centres of a second thermophilic strain, Synechococcus sp. OD24, gave square lattices (a = b = 14.5 nm; P2(1)). Irrespective of the packing arrangement, projections of negatively stained photosystem I complexes showed elongated asymmetric shapes with a large domain at one end which was tilted with respect to a small domain forming the tip of the other end. Such features were also found in averaged projections of solubilized reaction centre trimers. Surface reliefs reconstructed from freeze-dried metal-shadowed P2(1) lattices revealed that reaction centres had a ridge of 2.5 nm height projecting from one side of the membrane while their other side was rather flat and exhibited a shallow, central indentation.

Cyanobacteria↗
PubMed1988

Investigation of the structure of trimeric and monomeric photosystem I reaction centre complexes.

Electron microscopy of monomeric and trimeric forms of the reaction centre of photosystem I from the thermophilic cyanobacterium Phormidium laminosum has allowed the construction of a three-dimensional model describing the shape of the complex. The trimeric form of the Photosystem I reaction centre complex was found to have a very regular shape corresponding to a rounded equilateral triangle with edges 18 nm long and a thickness of 6 nm. A distinctive chiral arrangement of the three reaction centres in the trimer could be observed on one face of the complex, whereas the opposing face appeared to be smooth with no distinctive internal features. The monomeric reaction centre is roughly pearshaped, with a length of 15 nm and a width of 9 nm. A thickness of 6 nm is assumed from comparison with the trimer. It is predicted to lie with its shortest axis spanning the membrane. A double-lobed structure, with one lobe larger than the other, was occasionally observed for the monomeric reaction centre. No experimental evidence could be obtained for the existence of the trimeric form in the membrane. The formation of the trimeric form after detergent extraction is suggested. The trimeric form was found to be more stable than the monomeric form in solutions containing anionic and non-ionic detergents.

Journal Article↗
PubMed1987

Crystallization of the photosystem I reaction centre.

The reaction centre of the photosynthetic membrane complex photosystem I (PSI) from the thermophilic cyanobacterium Phormidium laminosum was found to crystallize under a range of conditions. The crystallization method, which can occur in the presence of larger detergent molecules than those used previously for the crystallization of membrane proteins, is presented in this report. Several crystal forms have been observed, and some of these show birefringence and linear dichroism. Optical measurements on crystals thicker than 5 microm were severely restricted because of the very high chlorophyll density within the crystals, but linear dichroism measurements on thin single crystals were possible and the results are presented here. By comparing the data with earlier measurements on oriented PSI complexes, a working model for the orientation of the PSI complexes within the crystal could be proposed. The PSI reaction centre is one of the largest and most complex membrane protein units that have been crystallized to date.

Journal Article↗
PubMed1981

Possible effects of the detachment of stromal lamellae from granal stacks on salt-induced changes in spillover. A study by sonication of chloroplasts.

Salt-induced chlorophyll fluorescence and spillover changes in control and briefly sonicated chloroplasts have been studied under conditions where Photosystem II traps are closed. In a low-salt medium containing 10 mM KCl, control envelope-free chloroplasts exhibited good spillover, as measured by low chlorophyll fluorescence yield at room temperature, a high ratio of the fluorescence peaks F735/F685 at 77 K, and increased Photosystem I activity in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and Photosystem II light. In contrast, when stacked chloroplasts were briefly sonicated and subsequently diluted into a low-salt medium, a high fluorescence yield at room temperature and a low ratio of F735/F685 at 77 K persisted. When unstacked chloroplasts were sonicated and then diluted into a high-salt medium, the room temperature fluorescence yield remained low. The results are interpreted in terms of a model relating the changes in chlorophyll fluorescence with the lateral diffusion of Photosystem I and Photosystem II chlorophyll-protein complexes in the plane of the thylakoid membrane creating randomized or segregated domains, depending on the degree of electrostatic screening of surface charges (Barber, J. (1980) FEBS Lett. 188, 1-10). It is argued that brief sonication of stacked chloroplasts separates stromal membranes from granal stacks, thus limiting the inter-mixing of the photosystems via lateral diffusion even when the ionic composition of the medium is varied. Consequently energy transfer from Photosystem II to Photosystem I is relatively poor and chlorophyll fluorescence from Photosystem II is enhanced. The loss of the salt effect on sonicated unstacked membranes can also be accommodated by the model. In this case it seems that the generation of small membrane fragments does not allow the normal salt-induced phase separation of the pigment-protein complexes to occur.

Chloroplasts↗
PubMed1981

Relationship between Thylakoid Membrane Fluidity and the Functioning of Pea Chloroplasts : EFFECT OF CHOLESTERYL HEMISUCCINATE.

Cholesteryl hemisuccinate has been incorporated into pea chloroplast thylakoids to investigate the relationship between fluidity and functioning of this membrane system. Levels of sterol which increased the apparent viscosity of the membrane, estimated by fluorescence polarization measurements using the lipophilic probe, 1,6-diphenyl-1,3,5 hexatriene, affected several photosynthetic processes. A decrease in fluidity was accompanied by an inhibition of dark limiting steps associated with electron transfer between photosystems two and one (PSII and PSI) as observed by the oxidation of the primary acceptor of PSII and by electron flow to ferricyanide. Also, treatment with cholesteryl hemisuccinate inhibited the saltinduced rise in chlorophyll fluorescence and changed the ionic conductivity of the membrane as judged by measurements of the decay of the lightinduced proton gradient. The results are discussed in terms of the effect of fluidity changes on the lateral diffusion of plastoquinone and chlorophyll protein complexes in the lipid matrix of the membrane.

Journal Article↗
PubMed1977

Phenylalanine metabolism and intellectual functioning among carriers of phenylketonuria and hyperphenylalaninaemia.

All members of 63 families who had phenylketonuric or hyperphenylalaninaemic offspring received a phenylalanine tolerance test and an individual intelligence test. Parent carriers (heterozygotes, n=115) displayed a significant relationship (canonical correlation R=0.75, P is less than 0.05) between their ability to metabolise phenylalanine and their intellectual strengths and weaknesses. Mothers of hyperphenylalaniaemic children did not show this relationship. The number of carrier children (n=40) was too small for multivariate or sex analysis, but significant bivariate correlations were found for this group.

Adolescent↗